Neural Code and Irregular Spike Trains

The problem of the code used by brain to transmit information along the different cortical stages is yet unsolved. Two main hypotheses named the

rate code

and the

temporal code

have had more attention, even though the highly irregular firing of the cortical pyramidal neurons seems to be more consistent with the first hypothesis. In the present article, we present a model of cortical pyramidal neuron intended to be biologically plausible and to give more information on the neural coding problem. The model takes into account the complete set of excitatory and inhibitory inputs impinging on a pyramidal neuron and simulates the output behaviour when all the huge synaptic machinery is active. Our results show neuronal firing conditions, very similar to those observed in

in vivo

experiments on pyramidal cortical neurons. In particular, the variation coefficient (CV) computed for the Inter-Spike-Intervals in our computational experiments is very close to the unity and quite similar to that experimentally observed. The bias toward the rate code hypothesis is reinforced by these results.